Research report 1999

PREFACE

This is our 6th web-based research report since we went
'online' in 1994. Since then, our website has attracted a lot of attention from all
over the world and meanwhile serves as an information source not only for our physics
colleagues and interested students but also for those out there, who simply want
to know on which subjects their 'tax Euros' are working. We appreciate the tremendous
activity on our server and do encourage everybody to come by and stay for a while- also: Why don't you leave a note in our guestbook?

This year, however, we slightly changed the appaerance of our report:
Instead of sub dividing our research activities into chapters we now cluster the
activities into the different research groups as shown on our homepage. We hope that
you can accustom to this new style.

OVERVIEW

Modern semiconductor technology nowadays combines more than ten
million different transistors on a single chip barely as big as a thumbnail to form
an extraordinary complex and sophisticated circuit. Following Moore's law, this very
large scale integration will proceed over roughly the next ten years until a single
element on a chip will be scaled down to less than about 50 nm. This typical dimension
of a single device, however, represents a barrier, beyond which the basic operation
of an electronic device starts to be based on fundamentally different mechanisms
as compared to the conventional ones.

In a classical silicon MOSFET, for example, the principle of operation
is based upon the statistical motion of about 10'000 electrons per square micron,
whose number may be varied by an external electrode via electric fields. This movement
takes place close to the relatively rough silicon/silicon dioxide interface and is
described by diffusive processes, similar to the Brown's motion of molecules.

If, however, the dimension of a device becomes comparable or even
smaller than the typical distance between two scattering events, the electrons start
to move ballistically, like the balls on a billiard table. Moreover, at these
small sizes, the number of electrons within a single device starts to approach one.
For even smaller devices, their size becomes comparable to the wavelength of the
electrons themselves - typically some ten nanometers in this case: The description
of the electrons behaving like little charged spheres starts to fail and to require
for a quantum mechanical formulation of the device.

In our group, we investigate the electronic, electrooptical,
and electromechanical properties of specially tailored semiconductor structures with
typical dimensions of the order or less than 100 nm. Recently, we also started to
process and investigate mechanical systems like resonators and oscillators on the
nanometer scale. Our goal is the detailed understanding of the new physical phenomena
associated with a dramatic reduction of size, to explore new grounds for future device
applications, and to be prepared for the day when nano-electronics will take
over the role of micro-electronicsand micro
or nano-mechanics will open new routes to the tiny ultra small universe!

- to boldly go where no person
has ever gone before !

The research in our group is based on three fundamental prerequisites
:

Nanotechnology

Sophisticated electronic and optical experimental
techniques

Quantum mechanical concepts and analysis

Starting from suited semiconductor layered systems, we first have to prepare
the desired structures with lateral nanometer size dimensions. We use and develop
different nanotechnologies that enable us to scale down the size of our structures
to the size of the electronic wavelength. For this purpose, our nanotechnology labs
are located in a dust free cleanroom area containing modern semiconductor processing
equipment.

As we're always trying to be internationally competitive, we set
up a large number of international co-operations with partners being specialized
in the epitaxial growth of our high quality starting material. Meanwhile, our nanotechnological
techniques are also transferred to different disciplines of leading edge research
resulting in newly developed collaborations with highly qualified specialists in
x-ray analysis, polymer physics and biophysics.

Secondly, we constantly develop and apply sensitive experimental techniques
which enable us to chararcterize and to investigate the electronic and optical properties
of our nanometer scale samples over the whole spectral range starting from DC over
the microwave and infrared regime, the visible spectrum up to UV. At the same time,
we are equipped with facilities allowing fo extremely low temperatures and high magnetic
fields - invaluable tools for the detailed understanding of the quantum mechanic
phenomena in our devices.

A third prerequisite for our research is a detailed and fundamental theoretical
analysis and understanding of nanophysics. Together with many theoretical groups
and in a very fruitful atmosphere of collaboration, we try to develop new theories
and techniques helping us to understand or to predict the many fascinating effects
that we are constantly facing. This is in particular important, as we are not studying
systems already existing in nature but try to artificially tailor small pieces
of this nature to behave in a desired fashion.